A role of pharyngeal length in obstructive sleep apnea patients

International Consensus Statement on Obstructive Sleep Apnea

BACKGROUND

Evaluation and interpretation of the literature on obstructive sleep apnea (OSA) allows for consolidation and determination of the key factors important for clinical management of the adult OSA patient. Toward this goal, an international collaborative of multidisciplinary experts in sleep apnea evaluation and treatment have produced the International Consensus statement on Obstructive Sleep Apnea (ICS:OSA).

METHODS

Using previously defined methodology, focal topics in OSA were assigned as literature review (LR), evidence-based review (EBR), or evidence-based review with recommendations (EBR-R) formats. Each topic incorporated the available and relevant evidence which was summarized and graded on study quality. Each topic and section underwent iterative review and the ICS:OSA was created and reviewed by all authors for consensus.

RESULTS

The ICS:OSA addresses OSA syndrome definitions, pathophysiology, epidemiology, risk factors for disease, screening methods, diagnostic testing types, multiple treatment modalities, and effects of OSA treatment on multiple OSA-associated comorbidities. Specific focus on outcomes with positive airway pressure (PAP) and surgical treatments were evaluated.

CONCLUSION

This review of the literature consolidates the available knowledge and identifies the limitations of the current evidence on OSA. This effort aims to create a resource for OSA evidence-based practice and identify future research needs. Knowledge gaps and research opportunities include improving the metrics of OSA disease, determining the optimal OSA screening paradigms, developing strategies for PAP adherence and longitudinal care, enhancing selection of PAP alternatives and surgery, understanding health risk outcomes, and translating evidence into individualized approaches to therapy.

Effect of tube length on the buckling pressure of collapsible tubes

BACKGROUND

The higher incidence of obstructive sleep apnea (OSA) in men than in women has been attributed to the upper airway being longer in men. The Starling resistor is the paradigm biomechanical model of upper airway collapse in OSA where a collapsible tube (representing the pharynx) is located between two rigid tubes (representing the nasal cavity and trachea). While the Starling resistor has been extensively studied due to its relevance to many physiological phenomena, the effect of tube length on tube collapsibility has not been quantified yet.

METHODS

Finite element analysis of a 3-dimensional collapsible tube subjected to a transmural pressure was performed in ANSYS Workbench. The numerical methods were validated with in vitro experiments in a silicone tube whose modulus of elasticity (361 ± 28 kPa) and dimensions (length = 100 mm, diameter = 22.2 mm, and wall thickness = 1.59 mm) were selected so that tube compliance was similar to pharyngeal compliance in humans during sleep. The buckling pressure (transmural pressure at which the tube collapses) was quantified in tubes of three different diameters (10 mm, 16 mm, and 22.2 mm) and ten length-to-diameter ratios (L/D = 4 to 13), while keeping the wall-thickness-to-radius ratio constant at 0.143.

RESULTS

The absolute value of the buckling pressure decreased from 4.7 to 3.3 cmH₂O (461-324 Pa) when L/D increased from 4 to 13. The buckling pressure was nearly independent from tube length for L/D >10.

CONCLUSIONS

Our finding that longer tubes are more collapsible than shorter tubes is consistent with the higher incidence of obstructive sleep apnea in males than females.

The relationship between three-dimensional craniofacial and upper airway anatomical variables and severity of obstructive sleep apnoea in adults

OBJECTIVE

The aim of this study was to evaluate the relationship between three-dimensional craniofacial and upper airway anatomical variables and severity of obstructive sleep apnoea (OSA) using cone beam computed tomography (CBCT).

METHODS

This was a prospective observational study, consisted of 95 adult OSA whose polysomnography and CBCT were available. Three-dimensional craniofacial and upper airway anatomical analysis were performed using 12 CBCT variables, including sagittal and vertical jaw relationships, maxillary width, the volume, length and minimum axial area of upper airway. The severity of OSA was evaluated through the apnea-hypopnea index (AHI). A hierarchical regression was performed to analyze the relationship between OSA severity and craniofacial and upper airway anatomical variables after controlling patients' demographic characteristics (gender, age, and BMI).

RESULTS

After controlling patients' gender, age, and BMI, individual CBCT variables including MAA, V-RPA, L-RPA and Go-Me were related to AHI. The final hierarchical regression model with demographic variables in Step 1 and CBCT variables (MAA, L-RPA and Go-Me) in Step 2 indicated that CBCT variables added additional explanatory power for AHI (ΔF(3,88) = 5.176, P = 0.002). Among these variables, L-RPA and Go-Me were statistically significant (P < 0.05).

LIMITATION

The OSA severity was expressed by AHI alone.

CONCLUSIONS

Three-dimensional craniofacial and upper airway morphology played an essential role in OSA severity. The most relevant anatomical characteristic with OSA severity were the length of retropalatal airway and mandibular body, which could be used to recognize severe OSA patients and as estimators for selecting the most appropriate treatment modality for OSA patients.

Oral Appliances in the Management of Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is a multifactorial condition, and an interdisciplinary approach to diagnosis forms the basis for effective treatment planning. Craniofacial structure and attached soft tissues and muscles play a central role in OSA. Evidence-based studies demonstrate the effectiveness of oral appliances for mandibular advancement and tongue stabilization in managing OSA, and current clinical standards of practice recommend the use of oral appliances to treat OSA when patients cannot tolerate continuous positive airway pressure (CPAP). Although effective, oral appliances are less predictable in managing OSA compared with CPAP therapy. Measures can be taken to improve predictability of oral appliance treatment.

Qualitative Phenotyping of Obstructive Sleep Apnea and Its Clinical Usefulness for the Sleep Specialist

INTRODUCTION

The anatomical collapsibility of the upper airway, neuromuscular tone and function, sleep-wake and ventilatory control instability, and the arousal threshold all interact and contribute to certain pathophysiologic features that characterize different types of obstructive sleep apnea (OSA). A model of qualitative phenotypizationallowsus to characterize the different pathophysiological traits in OSA patients.

METHODS

A narrative review was performed, to analyze the available literature evidence, with the purpose of generating a model of qualitative phenotypization to characterize pathophysiological traits in patients with OSA.

RESULTS

96 out of 3829 abstracts were selected for full-text review. Qualitative phenotyping model of OSA:Data concerning the OSA qualitative pathophysiological traits' measurement can be deducted by means of clinical PSG, grade of OSA severity, and therapeutic level of Continuous Positive Airway Pressure (CPAP) and are reported in the text. This approach would allow qualitative phenotyping with widely accessible methodology in a routine clinical scenario and is of particular interest for the sleep specialist, surgical treatment decision-making, and customized OSA multimodality treatment.

The Interaction Between Craniofacial Computed Tomographic Dimensional Parameters and BMI in Obstructive Sleep Apnea

Introduction

The impact of the dimensional parameters of the pharyngeal bony frame by its length, width and the position of the hyoid upon the severity of obstructive sleep apnea syndrome (OSAS) has not been investigated in depth. Interactions of those parameters with body mass index (BMI) and their overall reciprocal effect on OSAS severity have also not been established.

Materials and Methods

This retrospective cross-sectional study was conducted on 108 male OSAS patients followed in OSAS outpatient clinics between November 2014 and October 2015. They all underwent a polysomnography test, and an apnea-hypopnea index (AHI) was calculated. They also underwent an upper airway computerized tomographic scan in which three craniofacial parameters were evaluated: inter-pterygoid distance (IPD), hard palate-to-hyoid (HP-H) distance, and gnathion plane-to-hyoid (GP-H) distance.

Results

A longer pharynx and an inferiorly placed hyoid bone correlated with the AHI (r = 0.33, p = 0.001 and r = 0.226, p = 0.03, respectively). GP-H correlated with body mass index (BMI) (r = 0.3243, p < 0.001), while HP-H and IPD did not. We found an interaction between BMI and HP-H, but none between GP-H and BMI. IPD did not correlate with OSAS severity, but it correlates with the age of the OSAS patients (r = 0.235, p = 0.015).

Conclusion

Pharynx length and hyoid position have significant effects upon OSAS severity, and they interact differently with BMI in terms of those effects. Hard palate width increases with age but has no correlation with OSAS severity.

Oral Appliances in the Management of Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is a multifactorial condition, and an interdisciplinary approach to diagnosis forms the basis for effective treatment planning. Craniofacial structure and attached soft tissues and muscles play a central role in OSA. Evidence-based studies demonstrate the effectiveness of oral appliances for mandibular advancement and tongue stabilization in managing OSA, and current clinical standards of practice recommend the use of oral appliances to treat OSA when patients cannot tolerate continuous positive airway pressure (CPAP). Although effective, oral appliances are less predictable in managing OSA compared with CPAP therapy. Measures can be taken to improve predictability of oral appliance treatment.

The importance of obstructive sleep apnoea and hypopnea pathophysiology for customized therapy

The objective of this study is to highlight the importance of anatomical and not-anatomical factors' identification for customized therapy in OSAHS patients. The data sources are: MEDLINE, The Cochrane Library and EMBASE. A systematic review was performed to identify studies that analyze the role of multiple interacting factors involved in the OSAHS pathophysiology. 85 out of 1242 abstracts were selected for full-text review. A variable combinations pathophysiological factors contribute to realize differentiated OSAHS phenotypes: a small pharyngeal airway with a low resistance to collapse (increased critical closing pressure), an inadequate responses of pharyngeal dilator muscles (wakefulness drive to breathe), an unstable ventilator responsiveness to hypercapnia (high loop gain), and an increased propensity to wake related to upper airway obstruction (low arousal threshold). Identifying if the anatomical or not-anatomical factors are predominant in each OSAHS patient represents the current challenge in clinical practice, moreover for the treatment decision-making. In the future, if a reliable and accurate pathophysiological pattern for each OSAHS patient can be identified, a customized therapy will be feasible, with a significant improvement of surgical success in sleep surgery and a better understanding of surgical failure.

Mandibular morphology and pharyngeal airway space: A cephalometric study

Introduction

Mandibular retrognathism is considered to be the most important risk factor for upper airway obstruction.

Aim

This cross-sectional study intended to examine the relationship between craniofacial morphology and the pharyngeal airway space (PAS) in patients with mandibular retrognathism and mandibular prognathism, when compared to normal subjects. The study also analyzed the influence of mandibular morphology on pharyngeal length (PL).

Materials and Methods

The PAS was assessed in 92 females (age 15-30 years) further divided into three groups - Group 1- normal mandible (76°≤ SNB ≤82°; n = 31); Group 2-mandibular retrognathism (SNB <76°; n = 31); Group 3-Mandibular prognathism (SNB >82°; n = 30). All subjects were examined by lateral cephalometry with head position standardized using an inclinometer. Craniocervical angulation, uvula length, thickness and angulation were compared among different groups.

Results

The results showed no statistically significant difference in the pharyngeal airway between the three groups. Measurements of PL showed statistically significant higher values for retrognathic mandible group than normal and prognathic mandible group.

Conclusion

There is no significant difference between PAS between patients with mandibular retrognathism, normal mandible and mandibular prognathism. Mandibular retrognathism patients show a significantly higher uvula angulation than patients with mandibular prognathism. Craniocervical angulation showed maximum value in retrognathic mandible group followed by normal and prognathic mandible group respectively. Mean PL for retrognathic mandible patients was significantly higher than prognathic mandible patients.

Non-apneic snoring and the orthodontist: radiographic pharyngeal dimension changes with supine posture and mandibular protrusion

OBJECTIVE

To evaluate the radiographic changes that occur in the pharynx and surrounding structures with alteration of posture from the upright to the supine position and the effect that mandibular protrusion whilst supine has on these dimensions.

DESIGN

Prospective cephalometric study.

SETTING

University Dental Hospital and School.

SUBJECTS AND METHOD

This prospective study involved 35 consecutively referred adults with proven non-apneic snoring. Lateral skull radiographs were obtained with the subjects upright in occlusion, supine in occlusion and supine with the mandible protruded to the maximum comfortable position. Radiographs were traced and digitized, and the pharyngeal dimensional changes and hyoid position were examined. Males and females were examined separately.

RESULTS

Radiographic pharyngeal dimensions were changed with altered posture, resulting in significant reductions in the minimum post-palatal (p<0.01) and post-lingual (p<0.05) airway measurements in the supine position. Mandibular protrusion whilst in the supine position produced increases in the functioning space for the tongue.

CONCLUSION

A supine posture results in significant reductions in pharyngeal airway measurements of non-apneic snorers. Mandibular protrusion whilst in the supine position produces an increase in the functioning space for the tongue.

Obstructive sleep apnea

Obstructive sleep apnea (OSA) is a common disorder characterized by repetitive collapse of the pharyngeal airway during sleep. Control of pharyngeal patency is a complex process relating primarily to basic anatomy and the activity of many pharyngeal dilator muscles. The control of these muscles is regulated by a number of processes including respiratory drive, negative pressure reflexes, and state (sleep) effects. In general, patients with OSA have an anatomically small airway the patency of which is maintained during wakefulness by reflex-driven augmented dilator muscle activation. At sleep onset, muscle activity falls, thereby compromising the upper airway. However, recent data suggest that the mechanism of OSA differs substantially among patients, with variable contributions from several physiologic characteristics including, among others: level of upper airway dilator muscle activation required to open the airway, increase in chemical drive required to recruit the pharyngeal muscles, chemical control loop gain, and arousal threshold. Thus, the cause of sleep apnea likely varies substantially between patients. Other physiologic mechanisms likely contributing to OSA pathogenesis include falling lung volume during sleep, shifts in blood volume from peripheral tissues to the neck, and airway edema. Apnea severity may progress over time, likely due to weight gain, muscle/nerve injury, aging effects on airway anatomy/collapsibility, and changes in ventilatory control stability.

Development of a computational biomechanical model of the human upper-airway soft-tissues toward simulating obstructive sleep apnea

Numerous challenges are faced in investigations aimed at developing a better understanding of the pathophysiology of obstructive sleep apnea (OSA). The anatomy of the tongue and other upper-airway tissues, and the ability to model their behavior, are central to such investigations. We present details of the construction and development of a soft-tissue model of the human upper airway, with the ultimate goal of simulating obstructive sleep apnea. The steps taken to produce a representative anatomical geometry, of which the associated muscle histology is also captured, are documented. An overview of the mathematical models used to describe tissue behavior, both at a macro- and microscopic level, is given. A neurological model, which mimics the proprioceptive capabilities of the body, is described as it is applies to control of the active dynamics of the tongue. A simplified scenario, which allows for the manipulation of several environmental influences, is presented. It is demonstrated that the response of the genioglossus is qualitatively similar to that determined through experimental techniques. Furthermore, insights into the stress distribution developed within the tongue are discussed. It is shown that changes in almost any aspect of the breathing or physiological conditions invoke a significant change in the response of the airway dilators. The results of this study provide further evidence of the importance of modeling and simulation techniques as an aid in understanding the complex behavior of the human body.

Three-dimensional evaluation of upper airway in patients with different anteroposterior skeletal patterns

OBJECTIVES

To investigate variability in the upper airway of subjects with different anteroposterior skeletal patterns by evaluating the volume and the most constricted cross-sectional area of the pharyngeal airway and defining correlations between the different variables.

MATERIAL AND METHODS

The study sample consisted of 60 patients (29 boys, 31 girls) divided into three groups: Class I (1 ≤ ANB ≤ 3), Class II (ANB>3), and Class III (ANB<1), to evaluate how the jaw relationship affects the airway volume and the most constricted cross-sectional area (Min-CSA). Differences between groups were determined using the Tukey-Kramer test. Correlations between variables were tested using Pearson's correlation coefficient.

RESULTS

The volume and the Min-CSA of the pharyngeal airway (PA) were significantly related to anteroposterior skeletal patterns (p < 0.05). The nasopharyngeal airway (NA) volume of Class I and Class III subjects was significantly larger than that of Class II subjects (p < 0.05). The Min-CSA and the length of PA were significantly related to the volume of PA (p < 0.05). The site and the size of the Min-CSA varied among the three groups.

CONCLUSIONS

The volume and the most constricted cross-sectional area of the airway varied with different anteroposterior skeletal patterns. The NA volume of Class I and Class III subjects was significantly larger than that of patients with a Class II skeletal pattern.

Obstructive sleep apnea syndrome

Obstructive sleep apnea (OSA) syndrome is a common but often unrecognized disorder caused by pharyngeal collapse during sleep and characterized by frequent awakenings, disrupted sleep and consequent excessive daytime sleepiness. With the increasing epidemic of obesity, the most important risk factor for OSA, prevalence of the disease will increase over the coming years thus representing an important public-health problem. In fact, it is now recognized that there is an association between OSA and hypertension, metabolic syndrome, diabetes, heart failure, coronary artery disease, arrhythmias, stroke, pulmonary hypertension, neurocognitive and mood disorders. Diagnosis is based on the combined evaluation of clinical manifestations and objective sleep study findings. Cardinal symptoms include snoring, sleepiness and significant reports of sleep apnea episodes. Polysomnography represents the gold standard to confirm the clinical suspicion of OSA syndrome, to assess its severity and to guide therapeutic choices. Behavioral, medical and surgical options are available for the treatment. Continuous positive airway pressure (CPAP) represents the treatment of choice in most patients. CPAP has been demonstrated to be effective in reducing symptoms, cardiovascular morbidity and mortality and neurocognitive sequelae, but it is often poorly tolerated. The results of clinical studies do not support surgery and pharmacological therapy as first-line treatment, but these approaches might be useful in selected patients. A better understanding of mechanisms underlying the disease could improve therapeutic strategies and reduce the social impact of OSA syndrome.

Relations between obstructive sleep apnea syndrome and specific cephalometric measurements, body mass index, and apnea-hypopnea index

PURPOSE

To evaluate the relation of specific cephalometric landmarks, body mass index, and the apnea-hypopnea index in patients diagnosed with obstructive sleep apnea syndrome (OSAS) and treated with functional upper airway surgery.

MATERIALS AND METHODS

This was a retrospective cohort analysis of 89 consecutive patients over a 3-year period diagnosed with overnight-attended polysomnogram-confirmed OSAS who underwent functional upper airway surgery. Five predetermined specific cephalometric parameters were analyzed: posterior airway space, soft palate length, hyoid to mandibular plane angle, sella-nasion to mandibular plane angle, and gonion to gnathion length. Simple and multiple linear regression analyses were used to establish a relation between independent and dependent variables.

RESULTS

There were no statistically significant associations between the 5 specific cephalometric craniofacial structures in combination with other potential confounders, body mass index and apnea-hypopnea index, and the presence of OSAS.

CONCLUSIONS

No one skeletal or soft tissue parameter can be directly linked to OSAS.

Validity of upper airway assessment in children: a clinical, cephalometric, and MRI study

OBJECTIVE

To test the hypothesis that the capability of two-dimensional lateral cephalogram in recognizing pharyngeal obstruction is poor compared with the capability of three-dimensional magnetic resonance imaging (MRI) and clinical observation of tonsillar size.

MATERIALS AND METHODS

The study participants were 36 prepubertal children (19 male, 17 female; mean age 7.3 ± 1.43 years, range 4.8-9.8 years) with sleep-disordered breathing diagnosed by nocturnal polygraphy. Pharyngeal airway was imaged with a low-field open-configuration MRI scanner. Tonsillar size was clinically determined and lateral skull radiographs were taken and measured. Pearson correlation coefficients were calculated between the clinical, cephalometric, and MRI variables.

RESULTS

Nasopharyngeal and retropalatal cephalometric variables had a significant positive correlation with the MRI findings. Both techniques showed the narrowest measurement to be located in the retropalatal region. Clinical assessment of tonsillar size correlated inversely with MRI findings such as minimal retropalatal cross-sectional airway area (P  =  .000), minimal retroglossal cross-sectional airway area (P  =  .015), and intertonsillar airway width (P  =  .000). Cephalometric soft palate and tonsillar area correlated with clinical tonsillar size (P  =  .001).

CONCLUSIONS

The hypothesis is rejected. The findings confirm that the lateral cephalogram is a valid method for measuring dimensions of the nasopharyngeal and retropalatal region. When evaluating oropharyngeal size, clinical assessment of tonsillar size is a relatively reliable method.

Comparative effects of two oral appliances on upper airway structure in obstructive sleep apnea

STUDY OBJECTIVES

Oral appliances are increasingly being used for treatment of obstructive sleep apnea (OSA). Mandibular advancement splint (MAS) mechanically protrudes the mandible, while the tongue stabilizing device (TSD) protrudes and holds the tongue using suction. Although both appliances can significantly improve or ameliorate OSA, their comparative effects on upper airway structure have not been investigated.

DESIGN

Cohort study.

SETTING

Sleep Investigation Unit.

PATIENTS

39 patients undergoing oral appliance treatment for OSA.

INTERVENTIONS

OSA patients underwent magnetic resonance imaging (MRI) of the upper airway during wakefulness at baseline and with MAS and TSD in randomized order. Treatment efficacy was determined by polysomnography in a subset of 18 patients.

MEASUREMENTS AND RESULTS

Upper airway lumen and surrounding soft tissue structures were segmented using image analysis software. Upper airway dimensions and soft tissue centroid movements were determined. Both appliances altered upper airway geometry, associated with movement of the parapharyngeal fat pads away from the airway. TSD increased velopharyngeal lateral diameter to a greater extent (+0.35 ± 0.07 vs. +0.18 ± 0.05 cm; P<0.001) and also increased antero-posterior diameter with anterior displacement of the tongue (0.68 ± 0.04 cm; P<0.001) and soft palate (0.12 ± 0.03 cm; P<0.001). MAS resulted in significant anterior displacement of the tongue base muscles (0.35 ± 0.04 cm). TSD responders (AHI reduction ≥50%) increased velopharyngeal volume more than non-responders (+2.65 ± 0.9 vs. -0.44 ± 0.8 cm(3); P < 0.05). Airway structures did not differ between MAS responders and non-responders.

CONCLUSIONS

These results indicate that the patterns and magnitude of changes in upper airway structure differ between appliances. Further studies are warranted to evaluate the clinical relevance of these changes, and whether they can be used to predict treatment outcome.

Three-dimensional computed tomographic analysis of airway anatomy in patients with obstructive sleep apnea

PURPOSE

To identify abnormalities in airway size and shape that correlate with the presence and severity of obstructive sleep apnea (OSA).

MATERIALS AND METHODS

This was a retrospective case series of patients undergoing treatment of OSA who had preoperative computed tomographic (CT) scans of the upper airway available. Patients who had undergone CT scanning for nonairway pathologic features during the same period served as the controls. Digital 3D-CT reconstructions were made and 12 parameters of airway size and 4 of shape were analyzed. The posterior airway space, middle airway space, and hyoid to mandibular plane distance were measured on the lateral cephalograms of the patients with OSA. Bivariate analysis was used to identify the factors associated with the presence and severity of OSA as measured by the respiratory disturbance index (RDI). Multiple regression analysis identified the factors that correlated with the RDI.

RESULTS

Of the 44 patients with OSA, 15 (10 men and 5 women) had pre- and postoperative CT scans available. In addition, 17 patients (11 men and 6 women) were used as controls. The airway length was significantly increased in the patients with OSA (P < .01). On bivariate analysis, the length, lateral/retroglossal anteroposterior dimension ratio and genial tubercle to hyoid bone distance were associated with the RDI (P < .03). On multiple regression analysis, length (P < .01) had a positive correlation and the lateral/retroglossal anteroposterior dimension ratio (P = .04) an inverse correlation with the RDI.

CONCLUSIONS

The results of this study indicate that the presence of OSA is associated with an increase in airway length. Airways that were more elliptical in shape and mediolaterally oriented (greater lateral/retroglossal anteroposterior dimension ratio) had a decreased tendency toward obstruction.

Pathophysiology of sleep apnea

Sleep-induced apnea and disordered breathing refers to intermittent, cyclical cessations or reductions of airflow, with or without obstructions of the upper airway (OSA). In the presence of an anatomically compromised, collapsible airway, the sleep-induced loss of compensatory tonic input to the upper airway dilator muscle motor neurons leads to collapse of the pharyngeal airway. In turn, the ability of the sleeping subject to compensate for this airway obstruction will determine the degree of cycling of these events. Several of the classic neurotransmitters and a growing list of neuromodulators have now been identified that contribute to neurochemical regulation of pharyngeal motor neuron activity and airway patency. Limited progress has been made in developing pharmacotherapies with acceptable specificity for the treatment of sleep-induced airway obstruction. We review three types of major long-term sequelae to severe OSA that have been assessed in humans through use of continuous positive airway pressure (CPAP) treatment and in animal models via long-term intermittent hypoxemia (IH): 1) cardiovascular. The evidence is strongest to support daytime systemic hypertension as a consequence of severe OSA, with less conclusive effects on pulmonary hypertension, stroke, coronary artery disease, and cardiac arrhythmias. The underlying mechanisms mediating hypertension include enhanced chemoreceptor sensitivity causing excessive daytime sympathetic vasoconstrictor activity, combined with overproduction of superoxide ion and inflammatory effects on resistance vessels. 2) Insulin sensitivity and homeostasis of glucose regulation are negatively impacted by both intermittent hypoxemia and sleep disruption, but whether these influences of OSA are sufficient, independent of obesity, to contribute significantly to the "metabolic syndrome" remains unsettled. 3) Neurocognitive effects include daytime sleepiness and impaired memory and concentration. These effects reflect hypoxic-induced "neural injury." We discuss future research into understanding the pathophysiology of sleep apnea as a basis for uncovering newer forms of treatment of both the ventilatory disorder and its multiple sequelae.

Physiology of Sleep Disordered Breathing

Obstructive sleep apnea (OSA) results from complex interactions between anatomy and physiology. A structurally small and abnormally collapsible upper airway predisposes to disease, and interacts with normal and pathologic physiologic mechanisms to determine severity of disease. Understanding the pathophysiology provides insight into airway collapse, and may improve treatment and lead to potential new medical and surgical treatments for OSA.

Pathogenesis of obstructive sleep apnea

The pathogenesis of obstructive sleep apnea (OSA) has been under investigation for over 25 years, during which a number of factors that contribute to upper airway (UA) collapse during sleep have been identified. Structural/anatomic factors that constrict space for the soft tissues surrounding the pharynx and its lumen are crucial to the development of OSA in many patients. Enlargement of soft tissues enveloping the pharynx, including hypertrophied tonsils, adenoids, and tongue, is also an important factor predisposing to UA collapse, inasmuch as this can impinge on the pharyngeal lumen and narrow it during sleep. Other factors, including impairment of UA mechanoreceptor sensitivity and reflexes that maintain pharyngeal patency and respiratory control system instability, have also been identified as possible mechanisms facilitating UA instability. This suggests that OSA may be a heterogeneous disorder, rather than a single disease entity. Therefore, the extent to which various pathogenic factors contribute to the phenomenon of repetitive collapse of the UA during sleep probably varies from patient to patient. Further elucidation of specific pathogenic mechanisms in individuals with OSA may facilitate the development of new therapies that can be tailored to individual patient needs according to the underlying mechanism(s) of their disease.

The interaction between changes in upright mandibular position and supine airway size in patients with obstructive sleep apnea

INTRODUCTION

The purpose of this study was to investigate the interaction between upright mandibular position change and supine upper airway size in men with obstructive sleep apnea fitted with titratable oral appliances.

METHODS

Baseline supine cephalometry before placement of the oral appliance and after titration with the oral appliance in place were undertaken in 14 patients, and upright mandibular position change was evaluated with and without the titrated oral appliance in place with a DigiGraph workstation (Dolphin Imaging Systems, Valencia, Calif).

RESULTS

The apnea-hypopnea index was significantly reduced after titration of the oral appliance (P < .01). Upright mandibular position change was associated with significant vertical (P < .01) and horizontal (P < .01) mandibular repositioning. The size of the supine velopharynx (P < .05), but not the supine oropharynx, was significantly enlarged at the titrated mandibular position. The supine oropharyngeal size change was correlated with the upright horizontal repositioning of the mandible (r = 0.69, P < .01).

CONCLUSIONS

Evaluation of upright mandibular position changes with the DigiGraph workstation enables one to predict supine oropharyngeal enlargement with oral appliance therapy. Dose-dependent effects of the horizontal component of upright mandibular protrusion on supine oropharyngeal size in addition to velopharyngeal enlargement might contribute to oral appliance effectiveness in obstructive sleep apnea patients.

Obstructive Sleep Apnea: MR Imaging Volume Segmentation Analysis

PURPOSE

To retrospectively determine airway wall motion with volume segmentation of transverse cine magnetic resonance (MR) images in children with obstructive sleep apnea (OSA).

MATERIALS AND METHODS

Transverse fast gradient-echo cine MR images of the hypopharynx were obtained at 1.5 T in 31 children with OSA (eight girls, 23 boys; mean age, 11.3 years) and 21 children free of airway symptoms who underwent MR imaging for other clinical indications (11 girls, 10 boys; mean age, 3.5 years). Volume segmentation with a k-means clustering algorithm was applied to transverse cine MR images to quantify airway volumes at each time. Airway wall motion for each child was described with standard deviation and range. Coefficient of variance and normalized range, which are independent of airway size, were used to compare groups (Kruskal-Wallis test).

RESULTS

Plots of airway volume over time demonstrated large fluctuations during respiration in children with OSA and minimal fluctuations in controls; findings were consistent with airway distention and airway collapse in OSA. Average airway transverse volume was larger in the group with OSA than in the control group (OSA group, 2.52 mL; control group, 0.936 mL; P <.001). Mean standard deviation (OSA group, 0.840 mL; control group, 0.17 mL; P <.001) and mean range of airway cross section (OSA group, 3.552 mL; control group, 0.864 mL; P <.001) were larger in the group with OSA. Coefficient of variance (OSA group, 0.32; control group, 0.17; P <.001) and normalized range (OSA group, 1.42; control group, 0.96; P <.001) indicate statistically significant difference in airway dynamics in children with OSA.

CONCLUSION

Volume segmentation of transverse cine MR images of the hypopharynx aids in quantification of increased airway wall motion in children with OSA. Transverse MR imaging demonstrates both airway distention and collapse in children with OSA.

Acoustic pharyngometry patterns of snoring and obstructive sleep apnea patients

OBJECTIVE

Anatomic narrowing of the pharyngeal airway increases the relative negative pressure generated during inspiration, thus affecting the dynamic behavior of the upper airway. The aim of this work was to measure pharyngeal area in snoring patients with and without obstructive sleep apnea (OSA), as categorized by polysomnography and by acoustic pharyngometry, and to analyze the different curve patterns obtained from patients of both groups.

METHODS

We examined 50 snorers who were divided into 2 groups matched for age, gender, and body mass index.

RESULTS

Mean Apnea Index (AI) in nonapneic snorers (group 1) was 4, and mean pharyngeal area was 2.41 cm(2). In snoring patients with OSA (group 2), mean AI was 25.9 with a mean pharyngeal area of 1.589 cm(2) (P < 0.001). In both groups, the dependent variable (AI) can be predicted from a linear relation with the independent variable (pharyngeal area) with normality and constant variance tests passed. In group 1, the resulting curve can be 1 of 2 types depending on the relative area of the pharyngeal segment to the velopharyngeal area. In group 2, the curve pattern can be categorized into 3 patterns depending on the possible pathology of pharyngeal obstruction.

CONCLUSION

The acoustic reflection technique is reproducible, noninvasive, and free from potential side effects. The good correlation between AI and pharyngeal area adds to the potential of acoustic pharyngometry. Careful study of the pharyngeal cross-sectional area and curve topography may give a good idea about the site of upper airway obstruction.

Postural cephalometric analysis and nasal resistance in sleep-disordered breathing

OBJECTIVES

The study was designed to compare upright and supine cephalometric measurements in snorers and to evaluate the effects of mandibular position and nasal resistance on pharyngeal dimensions. Anthropometric, rhinomanometric, and cephalometric measurements were used to investigate predictors of apnea-hypopnea index.

STUDY DESIGN

Prospective, cross-sectional.

METHODS

Forty consecutive habitually snoring men waiting for nasal surgery (mean age, 44 y; mean body mass index, 28 kg/m2) underwent an overnight polysomnographic, anterior rhinomanometric, and cephalometric analysis in upright and supine positions.

RESULTS

Nasal resistance correlated positively with minimal pharyngeal airspace at the level of tongue. The opening of jaws after voluntary relaxation of the mandibular position on lying down correlated with decrease in pharyngeal airway measurements at both velopharyngeal and tongue-base levels. In stepwise multiple regression analysis the overall patient model explained 68% of the variation in apnea-hypopnea index with body mass index as the largest predictor. In the nonobese patients, the model explained 86% of variation in apnea-hypopnea index with change in anteroposterior position of the lower jaw in upright and supine measurements and combined nasal resistance after mucosal decongestion as independent determinants. In selected skeletal subtypes the models predicted 83%, 79%, 61%, and 90% of the variation in apnea-hypopnea index.

CONCLUSIONS

In the nonobese patients nasal resistance and change in mandibular position on lying down were found to be independent contributing factors to the apnea-hypopnea index. Further research on supine cephalometry and relaxed mandibular position may improve prediction of sleep-disordered breathing in snorers.

Evidence-based medicine in sleep apnea surgery

Since the first description of sleep apnea as a clinical entity, the understanding of it within the medical community has increased significantly. Much research has explored the causes, assessment, and treatment of this disease. This research has resulted in a variety of tools for assessment and approaches to treatment. As research progresses, new data have shed light on the strengths of traditional approaches and their limitations. This article gives background for current approaches and charts a potential future course for sleep apnea assessment and treatment.

Upper airway physiology and obstructive sleep-disordered breathing

Upper airway competence involves complex interactions between anatomy and physiology. The common final denominator of OSDB is a structurally small and abnormally collapsible upper airway. The mechanisms contributing are often an accumulation of many skeletal or soft tissue abnormalities and respiratory physiology that individually may or may not be pathologic. So far, simplistic models have hampered progress in this field. Successful medical and surgical treatment of OSDB continues to be elusive for too many patients. Great strides remain to be taken, but the possibility seems within reach.

The utility of cephalometry with the Muller maneuver in evaluating the upper airway and its surrounding structures in Chinese patients with sleep-disordered breathing

OBJECTIVE

The objective was to simultaneously measure the size and collapsibility of the upper airway in Chinese patients with sleep-disordered breathing using cephalometry with the Muller maneuver.

STUDY DESIGN

Prospective study of 100 consecutive Chinese patients evaluated for sleep-disordered breathing at a sleep center.

METHODS

Each patient received overnight polysomnography and two lateral cephalograms (at the end-expiration phase and the Muller maneuver, respectively) to evaluate the upper airway and its surrounding structures (soft palate, tongue, and hyoid bone). After excluding 15 subjects from this study because of unclear cephalograms, 85 patients with sleep-disordered breathing were enrolled, including 32 with snoring or mild obstructive sleep apnea and 53 with moderate to severe obstructive sleep apnea.

RESULTS

Patients with varying degrees of severity of sleep-disordered breathing significantly differed in terms of the structure and function of the upper airway and the surrounding structures. The Muller maneuver may result in dynamic changes in the retropalatal airway and pharyngeal length, and the levels of dynamic changes were related to the severity of sleep-disordered breathing. Pearson correlation analysis revealed that the decrease in the minimum retropalatal dimension during the Muller maneuver in patients with snoring or with mild obstructive sleep apnea was related to the thickening of the soft palate and posterior displacement of tongue. Meanwhile, the decrease in the minimum retropalatal dimension in patients with moderate to severe obstructive sleep apnea was related to lengthening of the soft palate, increased tongue height, and downward displacement of the tongue and hyoid bone.

CONCLUSION

Cephalometry with the Muller maneuver may provide further insight into the pathogenesis of various levels of severity of sleep-disordered breathing.

Upper airway motion depicted at cine MR imaging performed during sleep: comparison between young Patients with and those without obstructive sleep apnea

PURPOSE

To compare the patterns of dynamic airway motion depicted on cine magnetic resonance (MR) images obtained during sleep between young patients with and those without obstructive sleep apnea (OSA).

MATERIALS AND METHODS

Fast gradient-echo sequences were performed in the sagittal midline by using a 1.5-T unit to create cine MR images. Cine MR images obtained during sleep in 16 young patients with OSA were compared with those obtained in 16 young patients with no airway symptoms of airway disease. The nasopharynx, oropharynx, and hypopharynx were characterized in terms of airway motion as static patent (SP), dynamic patent, intermittent collapsed (IC), or static collapsed (SC); and the maximal diameter and greatest change in diameter (in millimeters) of these airways were calculated. Adenoid tonsil size and mouth position (ie, opened or closed) were determined. Differences in the frequency of MR imaging parameters in the different anatomic regions were evaluated by using Fisher exact, chi 2, and sample t tests.

RESULTS

There were statistically significant differences in the following parameters between the two groups: nasopharynx SP (P <.001) and IC (P <.001); hypopharynx SP (P <.001) and IC (P <.001); and mean change in airway diameter of the nasopharynx (P <.001) and hypopharynx (P <.001). The mean adenoid tonsil size in the patients with OSA was larger (P =.006).

CONCLUSION

There are significant differences in the patterns of dynamic airway motion between young patients with and those without OSA.

The male predisposition to pharyngeal collapse: importance of airway length

Obstructive sleep apnea is an important disorder because of both its prevalence and its cardiovascular and neurocognitive sequelae. Despite the fact that male sex is a major risk factor for this disorder, the mechanisms underlying this predisposition are unclear. To understand the pathophysiologic basis of the male predisposition for pharyngeal collapse, we performed a detailed analysis of the anatomic and physiologic features of the upper airway in a cohort of normal and near-normal subjects (equal number of men and women). Although no important physiologic (genioglossal electromyogram, airflow resistance) differences were observed between sexes, a number of anatomic differences were apparent. The pharyngeal airway length was substantially longer in men compared with women. There was also an increased cross-sectional area of the soft palate and an increased airway volume in men compared with women. Using signal-averaged anatomic data from male and female subjects, we developed representative male and female finite element airway models. This model demonstrated the male airway to be substantially more collapsible than the female airway, solely on the basis of anatomic differences. This study suggests that the male predisposition to pharyngeal collapse is anatomically based, primarily as the result of an increased length of vulnerable airway as well as increased soft palate size.

The effect of posture and a mandibular protruding device on pharyngeal dimensions: a cephalometric study

The objectives were to evaluate the impact of body posture on cephalometric measures and the level and the extent to which treatment with a mandibular protruding device (MPD) affects pharyngeal width. The study was composed of 77 patients: 50 were diagnosed with obstructive sleep apnea (OSA) and 27 snored. After each patient underwent a baseline medical (including a somnographic registration), dental and stomatognathic examination, an MPD that would protrude the mandible 75% of the maximal protrusion range was fabricated. In a radiographic examination, four cephalograms were taken: two in the upright position with and without the MPD and two in the supine position with and without the MPD. The cephalometric measures focused on the pharyngeal structures. MPD treatment significantly increased the relative pharyngeal area (at the level of the oropharynx and the hypopharynx) by a mean of +89.6 mm2 (P < 0.01) in the upright posture. The relative pharyngeal area, however, was reduced by more than 50% in the supine position compared with the upright position, independent of MPD treatment. In the supine position, compared with upright, most pharyngeal measures decreased significantly; the hyoid was significantly lower and displaced posteriorly, and the area of the velum increased by a mean of +201.2 mm2 (P < 0.001). We conclude that the MPD significantly increased most pharyngeal measures except the linear distance between the hyoid bone and the third vertebra and decreased the area of the velum.

Frontal and Lateral Cephalometry in Patients With Sleep-Disordered Breathing

OBJECTIVES/HYPOTHESIS

The traditional lateral-view cephalometric analysis is limited because it provides only two-dimensional analysis of the three-dimensional craniofacial structure. The objectives were to analyze lateral and frontal cephalometric radiographs in a series of normal patients and those with varying degrees of sleep-disordered breathing and to define the degrees of narrowing or other unfavorable anatomical changes that might differentiate the patients with sleep-disordered breathing from normal subjects.

STUDY DESIGN

A prospective study of 100 adult patients with sleep-disordered breathing and 60 age-matched normal subjects.

METHODS

An analysis of the lateral and frontal cephalometric measurements was performed to assess velopharyngeal anatomical features. A comparison was made between the patients' polysomnographic and cephalometric analyses.

RESULTS

The compromised cephalometric parameters that may be found in patients with sleep-disordered breathing include acute skull-base and bony nasopharynx angles, inferior hyoid position, thickening of the velum, reduced retrovelar posterior air space along with thickening of the velum, thickening of the posterior pharyngeal wall, and narrowing of the velopharyngeal lumen. Worsening of sleep-disordered breathing was generally associated with increased numbers of compromised cephalometric parameters. As body mass index increases, there is reduced velopharyngeal width, the velum thickness is increased, and the posterior pharyngeal wall thickness is increased.

CONCLUSIONS

Sleep-disordered breathing is associated with statistically significant changes in a number of cephalometric measurements. Frontal cephalometric analysis adds further information regarding the anatomical assessment of patients with upper airway obstruction, enhancing the traditional lateral cephalometric view.

The effects of orthognathic surgery on pharyngeal airway dimensions and quality of sleep

Orthognathic surgery has been associated with airway narrowing and induction of sleep-related breathing disorders. Therefore, the pharyngeal airway dimensions of 32 orthognathic surgery cases were prospectively investigated, and the relationship between the surgery and sleep quality assessed. Digitized lateral cephalometric radiographs were used to compare oropharyngeal airway morphologies before and after surgery. Patients were assessed in two main surgical groups based on sagittal jaw relationship. A questionnaire was used to assess changes in daytime sleepiness. The mandibular surgery cases were also assessed by overnight domiciliary sleep monitoring. A significant decrease in the retrolingual airway dimension was found in all patients after mandibular setback surgery and a significant increase in this dimension after mandibular advancement. The questionnaire and sleep study revealed no significant changes in snoring incidence or apnoeic events after mandibular setback surgery. For the mandibular advancement group, a change in sleep quality was found, but only in cases with signs of a pre-existing sleep disorder.

Dental considerations in upper airway sleep disorders: A review of the literature

STATEMENT OF PROBLEM

Upper airway sleep disorders are becoming recognized as common medical concerns. Multiple treatment options have been advocated, including the use of dental devices. Dental practitioners are being asked by the medical profession to become a part of the treatment team. This may be a challenging task because of the large number of dental devices available, rapid advancement in the understanding of this disease, and numerous publications.

PURPOSE

This article reviews the anatomic features and etiologic factors of upper airway sleep disorders and medical and dental treatment options.

METHODS

The literature review was conducted with an accepted literature research tool, PubMed, developed by the National Library of Medicine. Key words searched included "obstructive sleep apnea," "sleep apnea," "sleep disorders," and "snoring".

CONCLUSION

Dental devices are indicated in snoring and mild-to-moderate obstructive sleep apnea patients after medical evaluation and referral.

Predicting which Patients will Benefit from Surgery for Obstructive Sleep Apnea: The ENT Exam

Airway evaluation is critical for surgical decision making. In patients with obstructive sleep apnea (OSA), a minimal evaluation should include a basic head and neck physical examination to evaluate for overt pathology. An upper airway examination will also provide insight into identifying patients with a higher risk of OSA. For patients who are evaluated for surgery, endoscopy combined with cephalometrics is the most accepted method of identifying patients with retroglossal collapse and obstruction. A new paradigm suggests that most patients have multilevel obstruction, so examination should be directed at assessing risk factors to direct the aggressiveness of surgical intervention.

Role of pharyngeal length in patients with a lack of overbite

Anterior open bites may be localized dental manifestations, which are caused by habits or skeletal disharmony, with or without functional aberration. Previous studies suggest various associations between open bites and underlying etiologic factors. We hypothesize that respiratory efficiency may be associated with anterior open bites. Under the assumption that breathing efficiency of the oropharynx and hypopharynx may be related to pharyngeal airway length, a cephalometric variable, vertical airway length (VAL), was measured on lateral cephalograms obtained from a total of 58 subjects with, so called, "open bite tendencies" (hereafter, open bite tendency). By means of the variable VAL, the association between pharyngeal length and open bite was investigated. In addition, the difference between actual open bite and open bite tendencies was also examined. The samples were randomly collected under stringent selection criteria from an existing database. A series of statistical analyses, such as unpaired t test, multiple regression, and discriminant analysis, was used to test the proposed hypothesis. The study found that none of the open bite tendency indicators used can segregate open bite subjects from nonopen bite subjects. The obtained discriminant function clearly divides the samples into two groups, i.e., open bite group and nonopen bite group, which were based on VAL and lower facial height. The study concludes that, first, an open bite tendency may be a different entity from an actual open bite or may be a misconceptualized term. Second, pharyngeal length may be a convenient indicator to diagnose open bite. We speculate that open bite may be different from an open bite tendency in pharyngeal length.